A nonvolatile memory device having a rewritable nonvolatile memory is increasingly demanded mainly for a semiconductor memory card. The semiconductor memory card is high-price compared to an optical disk, media of tape, and the like, however, the demand as a recording medium is widely increasing for a portable apparatus such as a digital still camera and a mobile phone because of merits such as small-size, lightweight, vibration resistance, and easy handling. This semiconductor memory card has a flash memory as a nonvolatile main memory and has a memory controller for controlling the memory. The memory controller controls the flash memory on the reading and writing of data in accordance with reading and writing commands from the access device such as the digital still camera and a personal computer.
The flash memory incorporated in products, for example, the semiconductor memory card and a portable audio apparatus requires relatively long time to write and read data to and from a memory cell array, a storage unit. As a countermeasure to this, the flash memory is configured so that data in a plurality of memory cells can be collectively erased and so that data can be collectively written to a plurality of memory cells. The flash memory is composed of a plurality of physical blocks, and each physical block includes a plurality of pages. Data is erased in units of the physical blocks and is written in units of the pages.
Upon attaching the aforementioned nonvolatile memory device as a removal disc to the access device such as the digital still camera, the access device side manages the memory device by using a file system, for example, the FAT file system. The FAT file system manages file data in units of clusters by using a file allocation table (hereinafter referred to as a FAT). When file data is written to the nonvolatile memory device such as the semiconductor memory card, the FAT file system allocates the file data to an empty cluster by using the FAT, and further designates the file data and a cluster number (a logical address) allocated to the file data to the nonvolatile memory device.
In addition, Patent document 1 discloses in detail a nonvolatile memory system using such FAT file system. Patent document 1 discloses two types of file systems; one is a matched boundary file system which matches a boundary of a management region with a boundary of a data region in a logical address space and the other is an unmatched boundary file system which does not match the boundaries with each other.
As a property of the semiconductor memory, a data transfer speed is largely depended on storing statuses of data in physical blocks. In this respect, Patent document 2 discloses a technique by which an access device obtains a feasible data transfer speed from a nonvolatile memory device by restricting the description to a case of the matched boundary file system.    Patent document 1: Japanese Unexamined Patent Publication No. 2001-188701    Patent document 2: International publication No. WO05/015406